Typhloplanid flatworms (Mesostoma and related genera): Mechanisms of predation and evidence that they structure aquatic invertebrate communities

Mesostoma species and other typhloplanid flatworms are predators found in a wide variety of habitats. Laboratory observations of some Mesostoma spp found in shallow aquatic habitats (referred to as littoral species) have revealed a wide variety of prey killing mechanisms: 1) mucus trapping, 2) sit-and-wait predation, 3) releasing a toxin into the water, and 4) active searching. We review the existing literature on these mechanisms. We also describe for the first time the predatory behavior of a pelagic Mesostoma sp. found in Brazilian lakes.The existing literature is also reviewed to assess the potential impact of Mesostoma species and related genera on the aquatic invertebrate community. Mesostoma has a high potential for population increase and has been found in high densities in some shallow aquatic habitats. Single prey experiments show that a number of Mesostoma species feed heavily on mosquito larvae, some chironomid larvae and some daphnids but considerably less on most copepods and ostracods. Prey preference experiments reflect the same trends. Hence, these predation studies suggest that the flatworms, at high densities, should reduce populations of certain prey speces and, consequently, alter community structure. Field studies support this prediction. Mesostoma species, at high densities, appear to be important predators of mosquito larvae in shallow aquatic habitats even under conditions where high densities of planktivorous fishes had little impact. They also appear to alter zooplankton community structure. However, much of the field evidence is correlational and not experimental. No studies have assessed the impact of pelagic typhloplanids on zooplankton community structure.It is concluded that many more manipulative field experiments are needed to assess the impact of typhloplanids on aquatic invertebrate communities.     

中国涡虫一新纪录科(扁形动物门,单肠目,盲扁虫科)背睾涡虫属一新种

记述了中国涡虫单肠目1新纪录科背睾涡虫属1新种,即中国背睾涡虫Phaenocor asinensis sp.nov.。新种的主要鉴别特征是:外轮廓呈长子弹形,后缘呈刀切状;精巢长度占体长的2/3,位于卵黄腺的背部。阴茎表面小刺呈犬牙状,其内折部中段具4个矩形的粗刺。子宫有2个开口,一端连接卵巢,另一端连接生殖腔。卵黄腺呈条形,具短分支,左右卵黄腺无衔接。生活于淡水。标本保存在深圳大学生命科学学院形态学研究室。     

Two New Rhabdocoels (Platyhelminthes) from the Peruvian Amazon Floodplain

Two new Rhabdocoel species from the Peruvian Amazonia are described: Sergia calae n. sp. (Dalyelliidae) and Mesostoma ucamara n. sp. (Typhloplanidae). Both species were captured in the Pacaya-Samiria National Park, Loreto, Peru, with plankton-nets dragged several times through the abundant littoral floating plant-community. This is the first record of micro-turbellarians in this region. The discovery of these new species in the Pacaya-Samiria National Park suggests the high diversity of this area, which up to now has remained largely unknown, increases the general knowledge of the fauna of Neotropical turbellarians.